1. Field of the Invention
This invention generally relates to the field of color characterization of output devices, and specifically relates to generation and use of a color transform for mapping colors from a device-independent color space to a device-dependent color space. The transform provides one-to-one mappings of colorimetrically accurate colors with enhanced color purity in the device-dependent color space.
2. Description of the Related Art
In general, color characterization of output devices consists of generating a target consisting of color patches to effect a sampling of the gamut of the color device, and then building a source map (or forward model) from the device-dependent color space of the device to a device-independent color space based on the target of patches. To generate a destination map (or inverse model), defined as a map from the device-independent color space back to the device-dependent color space, the process of inversion of the forward model is required.
A commonly occurring phenomenon encountered during the inversion of a forward model is that two or more different original device-dependent color values may result in the same, or colorimetrically equivalent, value in the device-independent color space. That is, there is in general no one-to-one correspondence between device-dependent and device-independent values of the forward model.
There are situations where one value, or solution, is preferred over others. As an example, in a device-dependent color space such as RGB, an RGB solution of exactly RGB=(0,0,0) or RGB=(255,255,255) as values is preferred over one that has intermediate values falling in between 0 and 255. Among other things, a value of 0 or 255 does not need to be dithered on a halftone printer, a desirable feature if one is trying to print black text, for example. Another reason is to achieve the exact inverse of the forward model so that when the forward model is applied followed by the inverse model, the original RGB value is recovered.
A need therefore arises in a case where two or more different original device-dependent color values result in the same or colorimetrically equivalent value in the device-independent color space, for determining which of the two or more values is preferred.